Unpleasant malodors are derived from various sources, for example, daily environments, a variety of institutions such as factories, excrement (human waste) treating plants, waste disposal plants, cattle breeding farms (animal quarters) and others, and cause a malodor pollution.
As the substances or sources which cause such malodors, there may be mentioned a large number of compounds, for instance, nitrogen-containing compounds such as ammonia, amines (e.g. trimethyl amine, triethylamine, etc.), sulfur-containing compounds such as hydrogen sulfide, mercaptans (e.g. methyl mercaptan, etc.), aldehydes (formaldehyde, acetaldehyde, etc.), lower fatty acids (formic acid, acetic acid, propionic acid, valeric acid, etc.) and so on.
For removal of such malodorous components, an activated carbon is generally employed. However, the activated carbon, as it is, is deficient in an adsorption capacity relative to ammonia and other nitrogen-containing compounds, and to hydrogen sulfide and other sulfur-containing compounds. For this reason, an adsorbent (adsorbing agent) comprising an activated carbon supporting a halide, a metal ion, an acid, an alkali or others has been proposed. Such adsorbent, however, does not exhibit a sufficient deodorizing capability yet.
Further, zeolite, silica gel, an activated alumina and the like are also utilized as deodorizing agents. They are, however, deficient in adsorption capacity. In addition, inorganic adsorbents such as a zinc oxide, a magnesium oxide, an iron oxide, an iron hydroxide and others are also employed, but these adsorbents have insufficient adsorptivities to ammonia gas, although they are capable of, and suitable for adsorption and/or removal of hydrogen sulfide. Contrary to this, a zirconium oxide, a zirconium phosphate, a titanium oxide and the like are deficient in adsorption capacity to hydrogen sulfide, although they are excellent in adsorption of gaseous ammonia.
As described above, conventional deodorants and adsorbents are effective to either one of an acidic component or a basic component, but exhibit an insufficient deodorizing effect for the other component see for example Japanese Patent Application Laid-open Nos. 47445/1989 (JP-A-64-47445), 51421/1980 (JP-A-55-51421), 137089/1978 (JP-A-53-137089), 156539/1983 (JP-A-58-156539), 146578/1984 (JP-A-59-146578), 22074/1988 (JP-A-63-22074), 148340/1989 (JP-A-1-148340), 151938/1989 (JP-A-1-151938), 203040/1989 (JP-A-1-203040), etc.!
Japanese Patent Application Laid-open No. 54935/1988 (JP-A-63-54935) discloses an adsorbent as produced using TiO.sub.2, and Japanese Patent Application Laid-open No. 258644/1988 (JP-A-63-258644) discloses a deodorant comprising a mixture of a phosphoric acid or its salt, and iron (Fe), cobalt (Co), nickel (Ni), zirconium (Zr) or a compound of these metals, and a support such as an activated carbon on which the mixture is supported. These adsorbents are, however, insufficient in their adsorptivities (adsorbing capabilities).
WO91/08049 proposes a composition of a mixture of a water-insoluble titanium phosphate and a hydroxide of zinc or others. This composition demonstrates a comparatively high deodorizing capability relative to a malodorous component, but has yet insufficient adsorptivities to neutral malodorous components such as aldehydes.
On the other hand, it is known that a photocatalyst such as a titanium oxide provides deodorization of a malodorous component by oxidation and decomposition with an ultraviolet or other light irradiation. By way of illustration, Japanese Patent Application Laid-open No. 218635/1989 (JP-A-1-218635) discloses a deodorant containing an adsorbent such as an activated carbon, alumina and silica, and a photocatalyst such as a titanium oxide, a zinc oxide and a tin oxide. The purpose of such deodorant is to adsorb and decompose a malodorous component and thus to improve adsorption efficiency, and to insure the deodorizing effect over a long duration.
Further, deodorizing technologies using an oxide mixture containing a titanium oxide have also been proposed. For instance, Japanese Patent Application Laid-open No. 232966/1989 (JP-A-1-232966) discloses a deodorizing method by use of a photocatalyst in which an ultraviolet ray is irradiated in the presence of a mixture of metallic oxides comprising an oxide selected from the group consisting of iron titanate, an iron oxide, a bismuth oxide, a molybdenum oxide and a nickel oxide, and a titanium oxide in coexistence with a gas containing a compound capable of being oxidized and oxygen. Japanese Patent Application Laid-open No. 288321/1989 (JP-A-1-288321) discloses a deodorizing method which comprises, in the presence of a mixture of metallic oxides comprising either of a yttrium oxide or a tin oxide, and a titanium oxide, and a gas containing a compound capable of being oxidized and oxygen, irradiating an ultraviolet ray to the metallic oxide mixture. Japanese Patent Application Laid-open No. 288322/1989 (JP-A-1-288322) discloses a deodorizing method using a photocatalyst in which, in the presence of a mixture of metallic oxides comprising a titanium oxide and a magnesium oxide, and a gas containing a compound capable of being oxidized and oxygen, an ultraviolet ray is irradiated to the mixture of metallic oxides. Japanese Patent Application Laid-open No. 182205/1994 (JP-A-6-182205) discloses a photocatalyst obtained by supporting at least one member of particulates of gold, transition metals and rare earth elements on a metallic oxide such as a titanium oxide, treating the resultant product with ammonia and calcinating the treated product.
Use of these photocatalysts results in such an advantage that decomposition of aldehydes, which are hardly adsorbed, can be realized. They are, however, still insufficient in effects or capabilities as required for adsorbents. Therefore, when deodorization is conducted with the use of such photocatalyst, by-produced compounds associated with oxidation, for example, acetic acid by-produced with oxidation of acetaldehyde and the like, are permitted to release from the adsorbent into air again, and hence they would cause malodors. Further, a sufficient deodorizing effect can not be expected when deodorization is carried out without light irradiations. For this reason, malodorous components containing a neutral component in addition to an acidic component and a basic component can hardly be deodorized or removed completely with the use of the photocatalyst.